1. Field of the Invention
The field of the present invention is delayed coker drums, and more particularly a drumhead handling apparatus which is especially suitable for use with such drums, in view of the high pressures, high temperatures and dirty and hazardous conditions which prevail and the requirement of the drums for frequent and rapid opening.
2. Description of the Prior Art
Many refineries recover valuable products from the heavy residual oil that remains after the normal refining operations are completed. This recovery process, known as delayed coking, produces valuable distillates and coke in a large vessel called a coke drum. Typically, coke drums are used in pairs and operated alternately. Thus, while one coke drum is being filled with the heated residual oil for a 16 to 24 hour cycle in which the volatile components are driven off for recovery elsewhere and the balance converted to coke, the other drum is being cooled and purged of the several hundred tons of coke formed during the previous recovery cycle. The operating conditions are quite severe. Normal operating pressure ranges from 40 to about 60 pounds per square inch and the feed input temperature is slightly over 900.degree. F. In addition, operating personnel may be exposed to finely divided coke particles, steam, hot water and noxious gases, when the drum is opened.
Coke recovery operations commence following a water quench step. Steam and water are introduced into the coke filled vessel to complete the recovery of volatiles and cool the mass of coke. At this point, the vessel is vented to atmospheric pressure and the top head (typically a 4-foot diameter flange) is unbolted and removed to enable placement of the hydraulic coke cutting apparatus. After the cooling water is drained from the vessel, the bottom head (typically a 7-foot-diameter flange) is unbolted and removed to allow the hydraulically cut (i.e., high pressure water jet) coke to fall out. A typical operating procedures manual will state: "Protective rain gear and face shields must be worn when deheading top and bottom coke drumheads".
In a typical delayed coker processing system, as described and illustrated in commonly assigned U.S. Pat. No. 5,098,524, filed Jul. 29, 1988, entitled "Coke Drum Unheading Device", the first step in the current practice of removing coke involves placing a deheading cart under the drum, raising a flange support ram, with braces installed, and loosening some (up to one half) of the flange bolts by manual operation with an impact wrench. Following the water quench and drain, the remaining bolts are manually removed, braces are removed from the ram, the approximately 4-ton flange is lowered, and the cart, with flange resting thereon, is moved away.
The conventional coke drum deheading process is thus hazardous because of the required manual operations in conjunction with the drum, which holds a large quantity of coke that may be loose, and various amounts of hot water. In Antalffy, et al., U.S. Pat. No. 5,098,524, filed Jul. 29, 1988, entitled "Coke Drum Unheading Device", commonly assigned with this application, and in the paragraph entitled "Closure Apparatus Application Example" of U.S. Pat. No. 5,048,876 issued Sep. 17, 1991, entitled "Closure Apparatus for Pipes and Vessels", a system and process for removing the coke drumhead are described which provide an advantageous method of coke drum unheading in installations in which a relatively great amount of vertical space exists between the bottom of the drum and the floor. The drumhead is pivoted away from the drum by remote control means so that the drum may be opened without the need for human operators in the vicinity of the drumhead. There must be sufficient space between the bottom of the drum and the floor, however, to permit pivoting of the drumhead from the shut position to the fully opened position. In some delayed coker installations presently in use, the space between the bottom of the drum and the floor is as small as 4 1/2 to 5 feet, which is insufficient to permit pivoting of a drumhead of the type disclosed in pending application Ser. No. 5,098,524.
Thus, the need exists for a remote controlled coker unheading system that is suitable for use in installations where the distance between the drum and the floor is insufficient for pivoting of the drumhead.